problem in Gridview Paging by passing passing enum

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C#

ASP.NET

I have used gridview to bind data. in binding grid view i need two parameters,em getting both from query string but to make code more readable i have used enum everything is working fine but paging in gridview is not working my code is

 public static Enum TenderCategory;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            if (Convert.ToInt32(Request.QueryString["Category"]) == Convert.ToInt32(ValueTypeGroupEnum.ValueTypeGroup.State))
            {
                BindCategoryTenderList(ValueTypeGroupEnum.ValueTypeGroup.State, Convert.ToInt32(Request.QueryString["TenderCategoryID"]));
            }
        }
      }

private void BindCategoryTenderList(Enum TenderCategory, int TenderCategoryID)
    {
        try
        {
            TenderCategoryID = Convert.ToInt32(Request.QueryString["CategoryID"]);
            List<TenderManagement.Model.TenderDetail> tenderListByCategory = new List<TenderManagement.Model.TenderDetail>();
            tenderListByCategory = BLLTender.GetAllTenderByCategory(TenderCategory, TenderCategoryID);
            gvTenderListByCategory.DataSource = tenderListByCategory;
            gvTenderListByCategory.DataBind();
        }
        catch (Exception ex)
        { 

        }
    }

    protected void gvTenderListByCategory_PageIndexChanging(object sender, System.Web.UI.WebControls.GridViewPageEventArgs e)
    {
        gvTenderListByCategory.PageIndex = e.NewPageIndex;
        DataBind();
        BindCategoryTenderList(TenderCategory, Convert.ToInt32(Request.QueryString["CategoryID"]));
    }


 public static class ValueTypeGroupEnum
    {
        public enum ValueTypeGroup
        {
            Region = 1,
            Country = 2,
            State = 3,
            Ministry = 4,
            Organization_Type = 5,
            Product_Category = 6,
            Tender_Type = 8,
            Organization_Name = 10,
            City = 11,
            SubProductCategory=12
        }
    }

can anyone help plz...